Microelectronics chips such as integrated circuits are made from comparatively large wafers of semiconductor material. This process typically involves multiple successive steps including the following: generation of an etch mask photolithographically; etching of a layer of material as defined by the mask; removal of the photolithographic mask through some combination of wet and dry chemical techniques; removal of oxide layers prior to further processing; deposition of layers of materials; and rinsing to remove residual chemistry. The photolithographic mask is formed from a polymeric material called a photoresist. After the photoresist mask has been removed, a final cleaning step, called rinsing or wet cleaning is typically performed.
Deionized Water (DI-water) (i.e., ultrapure water) is known for its use in this rinsing of semiconductor devices. It is known to prevent any metal corrosion and contamination of the devices. It is desirable for the DI-water to contain very low levels of dissolved gases (e.g., nitrogen, oxygen, and carbon dioxide). Degassing systems can be used to remove dissolved gases from DI-water.
Diluted hydrofluoric acid can be used to remove oxide layers from silicon surfaces. Oxygen in etching liquid may oxide further silicon, which can result in removal of more silicon dioxide than a desired amount. Degassing the hydrofluoric acid used in creating diluted hydrofluoric acid can minimize the removal of extra silicon dioxide.
Gases typically used in the semiconductor industry can have a high degree of purity with a low content of water. A liquid source to be degassed can have a high vapor pressure. DI-water or water in diluted HF can have a vapor pressure that is a function of temperature. The vapor pressure can be higher than the water content (partial pressure) in semiconductor grade gases. Water in contact with semiconductor grade gases can cause some or all of the water to evaporate. For example, for a HF concentration of <0.5% at 25 degrees Celsius, a relative vapor pressure for water can be much higher than the vapor pressure for the HF in the HF concentration. It is desirable for a degas system that can prevent the evaporation of water.
Current vacuum degas systems include membrane contactors and water-ring vacuum pumps. Water-ring vacuum pumps can require an additional water supply. Current membrane based vacuum degas systems have a limited lifetime, thus they can need to be replaced every few years.
Some current degas systems are located at the site where DI-water is generated. In these systems the DI-water can be transported the through piping to the location where the DI-water is used. The DI-water piping can increase the amount of oxygen concentration in the DI-water, thus compromise the low level of oxygen concentration necessary for many semiconductor applications. The diffusion of oxygen through the piping can also limit process stability, as the oxygen concentration in the DI-water depends on the overall residence time of the water in the piping.